Integrated circuits include multiple intricate components that must be tested for compliance with design specifications. This is often done by applying a test signal to the digital circuitry within the integrated circuit to make sure that the circuitry performs as desired. The test signal is typically applied to a bonding pad on the integrated circuit.
Bonding pads are used to connect an integrated circuit to external devices and circuits. Thus, the bonding pads provide a conductive path to the digital circuitry within the integrated circuit. Bonding pads may be sensitive to damage from external probes. Thus, the probes used to apply the testing signal can potentially damage the bonding pads, thereby making the circuit unusable.
Damaged bonding pads can be especially wasteful with integrated circuits that include multiple wafers stacked on top of each other. For example, some three dimensional circuit technology involves bonding multiple circuits formed on separate wafers to each other. With such technologies, the circuit on each wafer is tested individually before it is bonded to another wafer. Thus, if the bonding pads are damaged during the testing, only that wafer can be discarded rather than the entire stack of wafers. But, a final test is still done when all wafers have been bonded to each other. If the bonding pad on the stack of wafers is damaged during testing, the entire stack of wafers may have to be discarded. Accordingly, it would be desirable to have a testing method that would involve less risk of damaging the bonding pads of an integrated circuit.